Since Apple introduced a mobile wallet on the iPhone in 2014, analysts have predicted that shoppers in bricks and mortar stores would soon routinely pay for jeans, groceries, and super-sized TVs with their phones.

But adoption of mobile payments by retailers has been slower than expected. Now Michael Taiano, director of the group focused on the financial industry at Fitch Ratings, says the transition maybe take even longer.

“This could be a multi-decade change that occurs,” Taiano tells Fortune, comparing the evolution of mobile payments to rise of e-commerce. Even after more than 20 years, e-commerce accounts for only 8% of all U.S. retail spending, he notes.

Taiano has been studying the potential of mobile payments as a possible disruptive force that could upset the status quo in banking. He published a report about the nascent industry spelling out some of the challenges on Monday.

Several hurdles have slowed the mobile payments revolution, he argues. One problem is that few companies offering mobile payments apps have given consumers an economic incentive to pay with their phone. Paying with an ordinary credit or debit card is easy and familiar—and accepted at most stores. Getting consumers to change may require giving them more of an incentive to use a mobile payment apps, Taiano says.

“It’s really about the value (proposition)—where is the value prop for mobile payments,” he says. Consumers are looking for discounts and rewards offers, but “up to now there really hasn’t been much.”

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That is slowly changing. Apple, Samsung, and others have pledged to incorporate retailer rewards programs into their payment apps, but progress has been extremely slow. This week, Samsung introduced its own rewards program so consumers who use its mobile payment app can earn points towards free gear and gift cards.

Another problem is the proliferation of different mobile payment apps. Technology companies like Apple, Googleand Samsung have created apps, as have banks such as JPMorgan Chaseand Citigroup, along with retailers themselves including Kohl’s and Walmart.

Too many options can create confusion, especially since different stores accept some but not all of the apps, Taiano says. Samsung Pay is the only app that can work at stores that have old-fashioned magnetic stripe readers at their cash registers, while Apple Pay requires a check out terminal equipped with a wireless NFC chip reader, for example. Some apps work only on Android while others can also work on the iPhone.

“There probably are too many out there now—it’s just confusing,” he says. Customers “don’t know what is accepted where.”